A solid-state image-capturing element such as CCD or CMOS to be used for a digital still camera attached to a cellular phone or a compact type digital still camera, has a spectral sensitivity of from visible region to a near infrared region in the vicinity of 1,100 nm. Accordingly, it is not possible to obtain a good color reproducibility as it is, and it is necessary to correct the luminosity factor by a filter cutting light in the near infrared region.
Heretofore, for such a filter, a phosphate glass containing CuO as an additive for selectively absorbing near infrared wavelength, has been employed. Such a glass contains a large amount of P2O5 and contains CuO as an essential component, and a large number of Cu2+ ions coordinated with oxygen ions are formed in an oxidating melting atmosphere, to show a blue green color, whereby the glass shows a near infrared cutting characteristics.
However, since a phosphate glass is insufficient in chemical durability (weather resistance), a weathering is formed on a polished glass surface, and it is difficult to use such a glass for a long time.
Accordingly, in order to improve chemical durability of phosphate glass, a fluorophosphates glass described in e.g. JP-A-1-219037 or JP-A-3-83834, that is produced by employing a fluorophosphate glass as a base glass and adding CuO to the base glass, has been developed.